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UNIVERSITI PUTRA MALAYSIA
MOHAMMAD HADI NEZHAD SHAHROKH ABADI
FK 2010 17
DEVELOPMENT OF NANOCRYSTALLINE THICK FILM GAS SENSORS
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DEVELOPMENT OF NANOCRYSTALLINE
THICK FILM GAS SENSORS
By
MOHAMMAD HADI NEZHAD SHAHROKH ABADI
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfillment of the Requirements for the Degree of Doctor of Philosophy
December 2010
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DEDICATION
To My Beloved: Mina, Zahra & Reza
My Mother Masoomeh & My Mother-in-Law Mansooreh
who their loves never end to me
and to the
Memories of My Father Ali, & My Father-in-Law Gholamreza
God Bless Them
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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirement for the degree of Doctor of Philosophy
DEVELOPMENT OF NANOCRYSTALLINE THICK FILM GAS SENSORS
By
MOHAMMAD HADI NEZHAD SHAHROKH ABADI
December 2010
Chairman: Mohd Nizar b Hamidon, PhD
Faculty: Engineering
In the last three decades along with growing industries and development of cities,
many pollutants have entered into the environment cycle. Some resultants of
these contaminations can be felt as air pollution. Now, many cities across the
world have been equipped with the databases to collect and analyze the
information related to air quality and to give the index of air pollution known as
API. In order to record and monitor the pollution, some of those databases use
advanced equipment and instrument which are very expensive and need regular
overhaul and maintenance. However, some databases are equipped with simpler
gas detectors, so-called solid state gas sensors.
Nowadays, many types of solid state gas sensors, employed different techniques
of fabrication, are released in the market. One of those techniques is known as
Thick Film Technology which has proved to be very promising and low cost
option to fabricate gas sensors for gas analyzers, but some problems still are
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associated to their efficiency such as deficient of selectivity, influence of
humidity, cross sensitivity, response time, and power consumption. The main
goal of this doctoral thesis is to develop a nanocrystalline metal oxide thick film
gas sensor using print screen technology having fast response time and highly
sensitive to air contaminants.
The fabricated gas sensor consists of a heater, an electrode, and a sensitive film
onto an alumina substrate, which can stand up to high firing temperature during
fabrication and operation. To fabricate the sensitive paste, tin dioxide (SnO2) and
tungsten trioxide (WO3) were used as the base powders. Meanwhile, platinum,
silver, and yttria (Y2O3) were used as additives and dopings. Finally, types of
alcohol (ethyl alcohol, isopropanol, and methanol), hydrocarbon (xylene,
isobutane), ketones (acetone), mixture of inorganic gases (exhaust fumes), and
wood smoke were applied to the sensors for measurement.
Fabrication of the sensitive paste has brought the development of a novel vehicle
binder in the organic phase of the paste. The novel binder fulfills the screen
printing criteria in which can be prepared very fast, having less additional
material with at least one month shelf life. Crystallite size of sensitive powder of
the sensors was measured using XRD analysis, showing sizes less than 30 nm
and 20 nm for metal oxide phase and metal additives, respectively. Low
dependency of WO3 sensors doped with Y2O3 to humidity was observed.
Sensitivity of fabricated sensors in the presence of applied gases was compared
to some commercial sensors and higher sensitivity was observed. The
0.9WO30.1Y2O3 sensor (WY-90) shows to be very sensitive to organic solvents
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compared with sensitivity of TGS2620 (Alcohol Sensor). The 0.98SnO20.02Pt
sensor (SnPt-980) shows to be more sensitive with faster response time to
organic solvents and truck exhaust gas than the commercial sensors of TGS2602
(Air Quality Taguchi Sensor), TGS3870 (Methane and Carbon Monoxide), and
TGS4160 (Carbon Dioxide). It shows a response time as low as 15 seconds in
the presence of 500 ppm exhaust gas compared to 28 seconds response time of
TGS2602.
Since the sensor is equipped with a heater element, it can operate at different
working temperatures and produce different sensing signal in the presence of
different gases or solvents, lead to have a selective gas sensor. Also, the
approach of screen printing fabrication eases the fabrication of an array of four
individual gas sensors with a very thin metal oxide and catalyst layer, using
pulse laser ablation deposition (PLAD) technique. The results show that the
response time of the array is significantly decreased to as low as 5 seconds in the
presence of 200 ppm acetone.
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Abstrak Tesis dihadapkan kepada Senat Universiti Putra Malaysia untuk keperluan kelayakan ijazah Doktor Falsafah
PENGEMBANGUNAN PENDERIA GAS FILEM TEBAL NANOKRISTALIN
Oleh
MOHAMMAD HADI NEZHAD SHAHROKH ABADI
Disember 2010
Ketua: Mohd Nizar b Hamidon, PhD
Faculti: Kejuruteraan
Dengan perkembangan industri dan pembangunan bandar semenjak tiga dekad
kebelakangan ini banyak bahan pencemar telah memasuki kitaran alam sekitar.
Ada di antara bahan pencemar ini yang boleh dirasai kehadirannya sebagai
pencemaran udara. Banyak bandar di seluruh dunia kini telah dilengkapi dengan
pangkalan data untuk mengumpul dan menganalisis informasi berkaitan dengan
tahap kualiti udara dan berfungsi untuk memberikan indeks pencemaran udara
(API) untuk merekod dan memantau pencemaran tersebut. Sesetengah pangkalan
data menggunakan peralatan dan instrumentasi yang maju tetapi berkos tinggi
serta memerlukan penyelenggaraan yang kerap. Tetapi terdapat juga pangkalan
data yang dilengkapi dengan penderia gas yang lebih ringkas iaitu penderia gas
berkeadaan pejal.
Kini, terdapat banyak jenis penderia gas berkeadaan pejal yang menggunakan
pelbagai teknik pembuatan yang terdapat di pasaran. Salah satu teknik ini
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dikenali sebagai Teknologi Selaput Tebal dimana ianya terbukti sebagai antara
pilihan yang meyakinkan serta berkos rendah untuk fabrikasi penderia gas.
Namunpun begitu ia masih mempunyai masalah berkaitan dengan kecekapan
seperti kekurangan di dalam pemilihan, pengaruh kelembapan, kepekaan rentas,
masa tindakbalas dan penggunaan tenaga. Objektif utama tesis doktorat ini ialah
untuk membangunkan “penderia gas selaput tebal nanokristal logam teroksida”
dengan menggunakan teknologi pencetak skrin yang mempunyai masa
tindakbalas yang pantas dan sangat peka terhadap unsur pencemar udara.
Penderia gas yang telah dibina mengandungi gelung pemanas dan filem sensitif
di atas alumina dimana ia boleh bertahan pada pemanasan suhu tinggi ketika
proses pembuatan dan semasa beroperasi. Untuk pembuatan bahan sebatian
sensitif penderia gas, tin dioksida (SnO2) dan tungsten trioksida (WO3)
digunakan sebagai bahan asas. Manakala, platinum, perak, dan yttria (Y2O3)
digunakan sebagai bahan penambah dan pengdopan. Akhir sekali, jenis-jenis
alkohol (ethyl alcohol, isopropanol, dan methanol), hydrocarbon (xylene,
isobutane), ketones (acetone), campuran gas bukan oraganik (gas ekzos), dan
asap daripada kayu telah digunakan terhadap penderia sebagai pengukuran.
Pembuatan bahan sebatian sensitif telah membawa kepada pembentukan
pembantu pengikat terkini di dalam fasa sebatian organik tersebut. Pembentukan
pembantu pengikat terkini yang memenuhi kriteria pencetakan skrin dimana ia
boleh disediakan dengan pantas, serta kurang penggunaan bahan tambahan dan
boleh digunakan dalam tempoh sebulan. Saiz hablur halus sensitif daripada
penderia telah diukur dengan menggunakan analisis XRD, dimana ia
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menunjukkan saiz kurang daripada 30 nm dan 20 nm untuk fasa oksida logam
serta bahan tambahan logam. Kurangnya kebergantungan penderia WO3 (yang
didopkan dengan Y2O3) terhadap kelembapan telah diperhatikan. Kadar kejituan
gas penderia dengan kehadiran gas telah dibandingkan dengan beberapa penderia
komersil yang sangat peka terhadap kehadiran gas. Penderia 0.9WO30.1Y2O3
(WY-90) menunjukkan kadar kepekaan yang tinggi terhadap bahan pelarut
organik berbanding dengan penderia TGS2620 (Penderia Alkohol). Penderia
0.98SnO20.02Pt (SnPt-980) menunjukkan kadar kepekaan yang tinggi dengan
masa tindakbalas yang lebih singkat terhadap bahan pelarut organik dan gas
daripada ekzos kenderaan berbanding penderia komersil TGS2602 (Air Quality
Taguchi Sensor), TGS3870 (Methane and Carbon Monoxide), dan TGS4160
(Carbon Dioxide). Ia menunjukkan masa tindakbalas masa serendah 15 saat
dengan kehadiran 500 ppm gas ekzos berbanding dengan 28 saat respon masa
oleh TGS2602.
Disebabkan penderia ini dilengkapkan dengan elemen gelung pemanas, ia boleh
beroperasi pada suhu yang berbeza-beza dan menghasilkan isyarat deria yang
berbeza bergantung kehadiran kepada jenis gas dan bahan pelarut. Ini
menunjukkan penderia gas ini bersifat selektif. Pendekatan teknik pembuatan
pencetak skrin juga telah digunakan bagi fabrikasi empat penderia gas individu
di dalam satu susunan dengan oksida logam dan lapisan pemangkin yang sangat
nipis menggunakan teknik Pulse Laser Ablation Deposition (PLAD). Keputusan
menunjukkan bahawa masa tindakbalas susunan empat penderia gas tersebut
jatuh secara signifikan sebanyak 5 saat dengan kehadiran 200 ppm acetone.
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ACKNOWLEDGEMENTS
I would like to express the deepest appreciation to my committee chair, Dr. Mohd Nizar
Hamidon, for his excellent guidance, caring, patience, and providing me with an
excellent atmosphere for doing research. He continually and convincingly conveyed a
spirit of adventure in regard to research and fellowship. I would like to thank Professor
Abdul Halim Shaari, who has the attitude and the substance of a genius, let me
experience the research of nanomaterials and gave me such a great opportunity to work
in his lab in the science faculty. Without his guidance and persistent help this
dissertation would not have been possible. I would like to thank my committee members
Dr. Norhafizah Abdullah and Dr. Norhisham Masiron for guiding my research for the
past three years and helping me to develop my background.
It is a pleasure to give especial thanks to Mr. Rahman Wagiran who believed me and
made this thesis possible and helped me with the research material. He provided a great
research grant supported by Ministry of Science, Technology and Innovation of
Malaysia (MOSTI). Without his corporation and supporting I could not have done my
research. Thank you very much Mr. Rahman.
I thank the University of Putra Malaysia for giving me the chance of being PhD student.
Thanks a lot to all of you guys. Also I would like to thank Mrs. Norita Hanapiah for
technical assistance in the thick–film laboratory and Mr. Ismail Ghani for macroscopic
measurements. Lastly, I offer my regards and blessings to all of those who supported me
in any respect during the completion of this doctoral research.
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APPROVAL SHEET I certify that a Thesis Examination Committee has met on 16 December 2010 to conduct the final examination of Mohammad Hadi Nezhad Shahrokh Abadi on his thesis entitled “Development of Nanocrystalline Thick Film Gas Sensors” in accordance with the Universities and University College Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The Committee recommends that the candidate be awarded the Doctor of Philosophy. Members of the Thesis Examination Committee were as follows: Fakhru`L-Razi b Ahmadun, PhD Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Roslina bt Mohd Sidek, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Alyani binti Ismail, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Neil White, PhD Professor University of Southampton United Kingdom (External Examiner)
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This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Doctor of Philosophy. The members of the Supervisory Committee are as follows: Mohd Nizar B Hamidon, PhD Faculty of Engineering Universiti Putra Malaysia (Chairman) Abdul Halim B Shaari, PhD Professor Faculty of Science Universiti Putra Malaysia (Member) Norhafizah bt. Hj. Abdullah, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member) Norhisam Misron, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)
_______________________________ HASANAH MOHD GHAZALI, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date:
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DECLARATION
I declare that the thesis is my original work except for quotations and citations which have been duly acknowledge. I also declare that it has not been previously and is not concurrently submitted for any other degree at Universiti Putra Malaysia or other institutions.
MOHAMMAD HADI SHAHROKH ABADI Date: 16 December 2010
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TABLE OF CONTENTS
Page
DEDICATION ii ABSTRACT iii ABSTRAK vi ACKNOWLEDGEMENTS ix APPROVAL x DECLARATION xii LIST OF TABLES xvi LIST OF FIGURES xvii ABREVIATIONS xxiii CHAPTERS
1 INTRODUCTION 1 1.1 Gas Sensors Demands and Motivation 1 1.2 Aim and Objective 4 1.3 Thesis Flow 4
2 GAS SENSORS DEVELOPMENTS 8
2.1 The Modern Gas Monitoring 9 2.2 Analytical Instruments and Monitoring Systems 10 2.3 Types of Gas Sensor 11
2.3.1 Infrared Gas Sensors 12 2.3.2 Photo-Ionization Gas Detectors 13 2.3.3 Solid State Gas 13 2.3.4 Catalytic Bead Gas 14 2.3.5 Electrochemical Gas Sensors 16 2.3.6 Optical Gas Sensors 17 2.3.7 Piezoelectric Gas Sensors 19 2.3.8 Field Effect Gas Sensors 20 2.3.9 Microelectromechanical Gas Sensors 22 2.3.10 Semiconductor Gas 24
2.4 Thick Film Resistive Gas Sensors 25 2.5 Operation Principle of TFRs 27
2.5.1 Bulk Conductivity Changes in TFR Gas Sensors 29 2.5.2 Surface Conductivity Changes in TFR Gas Sensors 32
2.6 Materials for Active Layer of TFR Gas Sensors 35 2.6.1 SnO2-Based Gas Sensors 37 2.6.2 WO3-Based Gas Sensors 40
2.7 Sensor Characteristics 43 2.7.1 Sensitivity of Gas Sensors 45 2.7.2 Selectivity of Gas Sensors 45 2.7.3 Stability of Gas Sensors 46 2.7.4 Response Time of Gas Sensors 47 2.7.5 Operating Temperature of Gas Sensors 48
2.8 Summary 48
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3 STATE OF THE ART OF THICK FILM TECHNOLOGY 49 3.1 History of Thick Film Technique 49 3.2 Comparison of Fabrication Techniques 50 3.2.1 Thick Film Technology 51
3.2.2 Thin Film Technology 52 3.2.3 Polymer or Soft Substrates 54 3.3 Fundamental of Thick Film Process 58 3.4 Design Aids 57
3.5 Screens 58 3.5.1 Mesh Materials 61 3.5.2 Screen Fabrication 62
3.6 Screen Printing 64 3.7 Thermal Curing Process 68 3.8 Thick Film Gas Sensor Fabrication 71
3.8.1 Alumina Substrate for TFR Gas Sensor 72 3.8.2 Gas Sensor Heater 73 3.8.3 Design of Electrodes 76 3.8.4 Fabrication of Thick Film Pastes 78
3.9 Summary 81 4 FABRICATION OF NANOCRYSTALLINE THICK FILM GAS SENSOR 82
4.1 Alumina Based-Substrate Thick Film Gas Sensor 82 4.2 Fabrication of Electric Parts 84 4.3 Fabrication of Organic Vehicle 86
4.3.1 Preparation of Conventional Organic Vehicle 87 4.3.2 Preparation of Novel Organic Vehicle Based-on Linseed Oil 88
4.4 Preparation of Binder 90 4.5 Preparation of Sensitive Layer 90
4.5.1 Sensitive Powder 91 4.5.2 Fabrication of Sensitive Paste 93 4.5.3 Thermal Treatment of Sensitive Film 94
4.6 Film Structure Monitoring 96 4.7 Bonding and Testing of the Sensor 97 4.8 Summary 100
5 CHARACTERIZATION OF NANOCRYSTALLINE THICK FILM GAS SENSORS 101
5.1 Characterization of Vehicle Binder 102 5.1.1 Organic Vehicle Based-on Ethyl Cellulose 102 5.1.2 Novel Organic Vehicle Based-on Linseed Oil 106
5.2 Characterization of Heater Element 109 5.2.1 Resistance of the Heater 109 5.2.2 Temperature Coefficient Resistance and Power
Consumption of the Heater 111 5.2.3 Thermal Response Time and Stability of Heater 114
5.3 Structural Analysis of Powders 115 5.3.1 X-Ray Diffraction (XRD) Analysis 115 5.3.2 Transmission Eelectron Microscopy (TEM) Studies 124
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5.4 Microstructural Analyses of Sensitive Films 127 5.4.1 Scanning Electron Microscopy (SEM) Studies 127 5.4.2 Energy-Dispersive X-Ray Spectroscopy (EDX) Studies 130
5.5 Gas Sensitivity Performance of the Sensors 133 5.5.1 WO3-Based Sensors 135 5.5.2 SnO2-Based Sensors 149 5.5.3 Sensitivity of WO3 and SnO2 Sensors to Humidity 163
5.6 Summary 164 6 Thick Film Laser Ablated Gas Sensor Array 166
6.1 Array Gas Sensor 166 6.2 Pulse Laser Ablation Deposition (PLAD) 169 6.3 Fabrication of Laser Ablated Array Gas Sensor 171 6.4 Characterization of Array Gas Sensor 173
6.4.1 X-Ray Diffraction (XRD) Analysis of SnO2 Pellet 174 6.4.2 Surface Analysis of Deposited Film 174 6.4.3 Gas Sensing Performance of Array 177
6.5 Summary 180 7 CONCLUSIONS AND FUTURE WORKS 181
7.1 Conclusion 181 7.1.1 Utilizing thick film technique to fabricate a gas sensor 182 7.1.2 Novel organic vehicle based-on linseed stand oil 182 7.1.3 Highly sensitive 0.9WO30.1Y2O3 sensor to Isobutane with low cross sensitivity to humidity 183 7.1.4 Highly sensitive nanocrystalline 0.99SnO20.01Pt thick film gas sensor for air quality applications 184 7.1.5 A fast response gas sensor array based-on thick film and pulse laser ablation deposition techniques 185
7.2 Future Works 186 REFERENCES 187 APPENDICES 206 BIODATA 222 LIST OF PUBLICATIONS AND AWARDS 223